Description:
An investigation of information within the CABRI program that relates to the possible roles of volatile fission products (as represented by cesium) will be described. This study was partially motivated by the observation of localized /sup 137/Cs concentration peaks in the axial gamma scans of pins pre-irradiated to about 5% burnup (B.U.) level. In order to evaluate potential effects of such concentrations, a re-examination of the existing test data for the 1% B.U. pins was performed. A comparison of CABRI hodoscope fuel motion results and the pre-CABRI /sup 137/Cs axial concentration profiles revealed an approximate spatial correlation between the initial points of fuels dispersal and cesium concentration enhancements (seven of eight cases). 9 figs.

Description:
Electron Beam diagnostics based on imaging techniques using Cherenkov conversion screens and intensified video cameras should be adaptable to the developing high-energy free-electron lasers (FEL) driven by radio frequency powered linear accelerators. The high beam energies (60-150 MeV) and the peak currents (100s of amps) anticipated should also make optical transition radiation intensities sufficient for these techniques. The distinctive features of the two light generation mechanisms will be summarized and a few diagnostic examples will be cited.

Description:
An improved understanding of High-Temperature Superconductors (HTSCs) should result from the direct investigation of the energy gap associated with the superconducting state. An adaptation of the classic transmission experiments using a broadly tunable Free- Electron Laser (FEL) to irradiate the HTSC single crystals or thin films as a function of photon energy and sample temperature is described. In particular, the Los Alamos FEL has a projected tuning range of 9-160..mu..m (140-8 MeV). In addition, its 10 to 20-ps micropulse structure, linear polarization, coherence, monochromaticity, focusability and peak power features should make it a unique research tool for probing HTSCs with critical temperature (T/sub c/) from /approximately/30 to /approximately/400 K (depending on the energy gaps involved). 14 refs., 4 figs., 2 tabs.

Description:
Selected optical diagnostics stations were upgraded in anticipation of low-emittance, bright electron beams from a thermionic rf gun or a photoelectric rf gun on the Advanced Photon Source (APS) injector linac. These upgrades include installation of optical transition radiation (OTR) screens, transport lines, and cameras for use in transverse beam size measurements and longitudinal profile measurements. Using beam from the standard thermionic gun, tests were done at 50 MeV and 400 to 650 MeV. Data were obtained on the limiting spatial ({sigma} {approximately} 200 {micro}m) and temporal resolution (300 ms) of the Chromox (Al{sub 2}O{sub 3} : Cr) screen (250-{micro}n thick) in comparison to the OTR screens. Both charge-coupled device (CCD) and charge-injection device (CID) video cameras were used as well as the Hamamatsu C5680 synchroscan streak camera operating at a vertical deflection rate of 119.0 MHz (the 24th subharmonic of the S-band 2856-MHz frequency). Beam transverse sizes as small as {sigma}{sub x} = 60 {micro}m for a 600-MeV beam and micropulse bunch lengths of {sigma}{sub {tau}}&lt;3 ps have been recorded for macropulse-averaged behavior with charges of about 2 to 3 nC per macropulse. These techniques are applicable to linac-driven, fourth-generation light source R and D experiments including the APS's SASE FEL experiment.

Description:
Particle-beam characterizations of a multi (7)-GeV storage ring beam have been done for the first time using a synchroscan and dual-sweep x-ray streak camera at the Advanced Photon Source (APS). The hard x-rays (2-20 keV) from a bending magnet source were imaged using an adjustable pinhole aperture, and both the horizontal size, {sigma}{sub x} {approximately} 190 {micro}m, and bunch length, {sigma}{sub t} {approximately} 28 ps, were measured simultaneously. The Au photocathode provides sensitivity from 10 eV to 10 keV covering the three orders of magnitude in wavelength from the UV to hard x-rays.

Description:
The Advanced Photon Source (APS) injector includes an S-band linac with the capability to accelerate beams to 650 MeV. The linac has recently been upgraded with the installation of an rf thermionic gun in addition to the standard DC thermionic gun. The rf gun is predicted to have lower emittance (5{pi}mm mrad) and may be used to support the APS self-amplified spontaneous emission (SASE) experiments. The critical characterization of this gun's beam has begun with a beam diagnostics station at the end of the linac that can address beam transverse size, emittance, and bunch length (peak current). This station uses both an optical transition radiation (OTR) screen at 45{degree} to the beam direction and a Ce-doped YAG single crystal normal to the beam with a 45{degree} mirror behind it. The visible light images are detected by a Vicon CCD camera and a Hamamatsu C5680 synchroscan streak camera. Spatial resolution of about 30 {micro}m ({sigma}) and temporal resolution of 1 ps ({sigma}) have been demonstrated. Examples of rf gun beam characterization at 220 MeV are reported.

Description:
The particle-beam imaging diagnostics for the Advanced Photon Source (APS) injector lime have been enhanced by the installation of optical transition radiation (OTR) screens and the use of Ce-doped YAG crystals as beam profile monitors. Both converters have improved spatial resolution and time responses compared to the standard Chromox (Al{sub 2}O{sub 3}:Cr) screens used elsewhere in the linac. These enhancements allow us to address the smaller beam sizes (&lt; 100 {micro}m) and the critical micropulse bunch length of higher brightness gun sources For the Linac macropulse of 30-ns duration composed of 86 micropulses at S-band frequency intervals, only the OTR mechanism is prompt enough to separate individual micropulses and to allow streak camera measurements of the micropulse averaged bunch length. Tests have been performed at 400 to 625 MeV using the gated DC thermionic gun source. Beam sizes less than {sigma}{sub x} = 30 {micro}m have been observed with a micropulse bunch length of {sigma} = 2-3 ps using OTR. First results on the lower-emittance rf thermionic gun are briefly discussed.

Description:
The measurement of bunch length and longitudinal profile for microbunches of electrons and positrons in the ps and sub-ps regime will be a critical part of validating performance of proposed facilities. Data will be presented showing single-sweep streak camera results at {sigma}{sub res} {approximately} 68 fs and projected synchroscan sweep resolution at {sigma} {approximately} 600 fs. Additionally, an rf cavity operating in a transverse magnetic mode has recently been shown to produce {sigma}{sub res} {approximately} 280 fs when used with a low-emittance beam. The potential for dual-sweep streak work with {sigma}{sub res} < 1 ps on the fast axis is also described.

Description:
The x-ray pinhole camera diagnostics on the Advanced Photon Source (APS) storage ring have recorded an effective transverse beam size instability during operations with a sextuplet plus 22 singlets fill pattern. These instabilities were not observed with the sextuplet plus 25 triplets fill pattern that has been the standard fill pattern in FY'98. The instability threshold is at 82-85 mA with positrons. The features include an increased average (few seconds) transverse size both horizontally and vertically for stored currents above the threshold with a correlated effect on the beam lifetime. The horizontal transverse emittance is 25-30% larger at 100 mA than below the threshold. There is a related horizontal beam centroid motion as well, but this does not explain the vertical size change nor the lifetime effect. Complementary data were also taken with the diagnostic undulator, and a similar threshold effect on divergence was observed. The cross-comparison of the data and possible mechanisms is presented.

Description:
An overview of particle and photon beam bunch length measurements is presented in the context of free-electron laser (FEL) challenges. Particle-beam peak current is a critical factor in obtaining adequate FEL gain for both oscillators and self-amplified spontaneous emission (SASE) devices. Since measurement of charge is a standard measurement, the bunch length becomes the key issue for ultrashort bunches. Both time-domain and frequency-domain techniques are presented in the context of using electromagnetic radiation over eight orders of magnitude in wavelength. In addition, the measurement of microbunching in a micropulse is addressed.

Description:
The LASL pinhole-intensified TV system was used at the TREAT reactor to image an internally vented, fuel-ejection capsule designed and built by HEDL. Several improvements in the imaging system over PINEX-1 were incorporated. A sequence of 16-ms TV frames shows axial expansion, expulsion of fuel from the pin, and retention of clad integrity during the time of coverage.

Description:
A preliminary design for the adaptation of a pinhole experiment (PINEX) technique to the monitoring of the dynamics of high temperature plasmas is described. Specifically, this imaging technique uses a thick aperture, an efficient radiation converter, and highly intensified television cameras to provide real-time viewing of radiation sources such as the neutron emissions from d-d and d-t fusion reactions in controlled thermonuclear research devices. The neutron emission strengths, R approx. 5 x 10/sup 15/ n/s, recently achieved at the Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET) should be sufficient for 3 to 6-cm spatial resolution and 10 to 100-ms time resolution using such a system. Such information should be useful for on-line optimization of the plasma and for quantitative evaluation of its performance.

Description:
The applications of ''streak systems'' that provide time-resolved diagnostic data for the Los Alamos free-electron laser energy recovery experiments have been extended in the last year. We have used these systems with time resolutions of 10 ..mu..s, approx.20 ps, and 2 to 8 ps to address both macropulse and micropulse issues. As one example, the time-dependent extraction efficiency behavior during the macropulse is presented. In addition, the effects on the electron micropulse temporal shape of several accelerator parameters have been studied. These results include the evidence of electron beam peak currents that approach 200 A.

Description:
A background source of electrons from the photoelectric injector (PEI) of the Los Alamos FEL experiment has been identified. This source is present without the drive laser irradiation and when the rf power is applied to the injector accelerator. Using intensified cameras and a synchroscan streak camera, these electrons have been imaged via optical transition radiation and Cherenkov radiation and characterized. The basic questions of location (photocathode), timing ({approximately} 40 to 90 {degree} of the rf cycle), magnitude (2.2 nC per {mu}s of rf power at 26 MV/m at the photocathode), and parameter sensitivity (accelerator A field's duration and magnitude) have been answered. The properties are consistent with a field-emission mechanism. 3 refs., 4 figs.

Description:
The on-line extraction efficiency analysis procedures for the Los Alamos Free-Electron Laser are described. The analyses are based on the measurement of the electron beam's energy spectron as a function of time under lasing and nonlasing conditions. In the nongraphic, tuneup mode the procedure takes about six seconds, so at a 1 Hz repetition rate for the laser we can analyse one out of every six shots. If graphics output is desired, it is produced at a 20-s repetition rate. The tapered wiggler result for extraction efficiency, eta approx. 2% is presented as an example.

Description:
Several unique time-resolved imaging techniques have been developed to address radio frequency (RF)-linac generated electron beams and the free-electron lasers (FEL) driven by such systems. The time structures of these beams involve a series of micropulses with 10 to 15-ps duration, separated by tens of nanoseconds. Mechanisms to convert the e-beam information to optical radiation include optical transition radiation (OTR), Cherenkov radiation, spontaneous emission radiation (SER), and the FEL mechanism itself. The use of gated, intensified television cameras and synchroscan and dual-sweep streak cameras to time-resolve these signals has greatly enhanced the power of these techniques. A brief review of the less familiar conversion mechanisms and electro-optic techniques is followed by a series of specific experimental examples from the RF linac FEL facilities at Los Alamos and Boeing (Seattle, WA). 23 refs., 35 figs., 3 tabs.

Description:
The Advanced Photon Source (APS) will be a third-generation synchrotron radiation (SR) user facility in the hard x-ray regime (10--100 keV). The design objectives for the 7-GeV storage ring include a positron beam natural emittance of 8 {times} 10{sup {minus}9} m-rad at an average current of 100 mA. Proposed methods for measuring the transverse and longitudinal profiles will be described. Additionally, a research and development effort using an rf gun as a low-emittance source of electrons for injection into the 200- to 650-MeV linac subsystem is underway. This latter system is projected to produce electron beams with a normalized, rms emittance of {approximately}2 {pi} mm-mrad at peak currents of near one hundred amps. This interesting characterization problem will also be briefly discussed. The combination of both source types within one laboratory facility will stimulate the development of diagnostic techniques in these parameter spaces.

Description:
Time-resolved experiments on rf-linac driven free-electron laser (FEL) experiments have recently been extended to displaying both the submicropulse and submacropulse effects. By using a synchroscan sweep on a streak camera key rf phase effects can be studied, and an additional dual sweep feature can provide this information during the macropulse. Successful measurements to date on the Los Alamos and Boeing FELs include electron-beam micropulse bunching during a macropulse, phase stability effects, micropulse elongation and transit time in a photoinjector, drive-laser phase stability, and FEL output evolution. Several of these measurements are the first of their kind on a FEL system 7 refs., 10 figs., 1 tab.

Description:
The usefulness of imaging electro-optics for rf-driven accelerators can be enhanced by synchronizing the instruments to the system fundamental frequency or an appropriate subharmonic. This step allows one to obtain micropulse bunch length and phase during a series of linac bunches or storage ring passes. Several examples now exist of the use of synchroscan and dual-sweep streak cameras and/or image dissector tubes to access micropulse scale phenomena (10 to 30 ps) during linac and storage ring operations in the US, Japan, and Europe. As space permits, selections will be presented from the list of phase stability phenomena on photoelectric injectors, micropulse length during a macropulse, micropulse elongation effects, transverse Wakefield effects within a micropulse, and submicropulse phenomena on a stored beam. Potential applications to the subsystems of the Advanced Photon Source (APS) will be briefly addressed.

Description:
The feasibility of using the optical transition radiation (OTR) generated as a 11.4- to 300-MeV/u ion beam passes through a single metal conducting plane for a minimally intercepting beam profile monitor for GSI/Darmstadt has been evaluated for the first time. Although these are non-relativistic beams, their beta and gamma values are similar to the 80-keV electron-beam imaging studies previously done on the CTF3 injector. With anticipated beam intensities of 10{sup 9} to 10{sup 11} particles per pulse and the predicted charge-squared dependence of OTR, the ion charge state becomes a critical factor for photon production. The OTR signal from the ion charge integrated over the video field time should be comparable to or larger than the CTF3 electron case. These signal strengths will allow a series of experiments to be done that should further elucidate the working regime of this technique.

Description:
At the Fermilab A0 photoinjector facility, bunch-length measurements of the laser micropulse and the e-beam micropulse have been done in the past with a single-sweep module of the Hamamatsu C5680 streak camera with an intrinsic shot-to-shot trigger jitter of 10 to 20 ps. We have upgraded the camera system with the synchroscan module tuned to 81.25 MHz to provide synchronous summing capability with less than 1.5-ps FWHM trigger jitter and a phase-locked delay box to provide phase stability of {approx}1 ps over 10s of minutes. This allowed us to measure both the UV laser pulse train at 244 nm and the e-beam via optical transition radiation (OTR). Due to the low electron beam energies and OTR signals, we typically summed over 50 micropulses with 1 nC per micropulse. We also did electron beam bunch length vs. micropulse charge measurements to identify a significant e-beam micropulse elongation from 10 to 30 ps (FWHM) for charges from 1 to 4.6 nC. This effect is attributed to space-charge effects in the PC gun as reproduced by ASTRA calculations. Chromatic temporal dispersion effects in the optics were also characterized and will be reported.

Description:
Designs are being developed to produce diffraction-limited sources based on storage-ring free-electron lasers (FELs) for the VUV and soft x-ray regime and linac-driven FELs in the few {Angstrom} regime. The requirements on the beam quality in transverse emittance (rms, normalized) of 1-2 {pi} mm mrad, bunch length (1 ps to 100 fs), and peak current (1 to 5 kA) result in new demands on the diagnostics. The diagnostics challenges include spatial resolution (1-10 {mu}m), temporal resolution (<100 fs), and single-pulse position measurements ({approximately}1 {mu}m). Examples of recent submicropulse (slice) work are cited as well as concepts based on spontaneous emission radiation (SER). The nonintercepting aspects of some of these diagnostics should also be applicable to high-power FELs.

Description:
At the Fourth Generation Light Source Workshop in January 1996, storage-ring-based FELs and linac-based FELs were considered for VUV/soft x-ray and hard x-ray ({lambda} {approximately} 1 {angstrom}) photon production, respectively. The general requirements of a diffraction-limited source--bunch lengths less than 1 ps (100 fs in case of the linac-based source), coherence, and a brightness several orders of magnitude brighter than third-generation sources--were among the features discussed. Examples of progress in demonstrations, measurements, or calculations that support research towards these areas are cited. These range from the 50-fs bunch length measurement at low current in a linac to few-{micro}rad divergence measurements on a 7-GeV storage ring. The possible extension of transition radiation beam characterization techniques to nonintercepting diffraction radiation is briefly addressed as well.

Description:
Initial commissionings of the Advanced Photon Source (APS) 7-GeV storage ring and its diagnostics systems have been done. Early studies involved single-bunch measurements for beam transverse size ({sigma}{sub x} {approx} 150 {mu}m, {sigma}{sub y} {approx} 50 {mu}m), current, injection losses, and bunch length. The diagnostics have been used in studies related to the detection of an extra contribution to beam jitter at {approximately} 6.5 Hz frequency; observation of bunch lengthening ({sigma} {approx} 30 to 60 ps) with single-bunch current; observation of an induced vertical, head-tail instability; and detection of a small orbit change with insertion device gap position. More recently, operations at 100-mA stored-beam current, the baseline design goal, have been achieved with the support of beam characterizations.

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